The assemblies formed of a cylindrical part pressed into a tubular part of the above kind in a cruciform arrangement can have applications in themselves, in particular by virtue of the particular assembly of the parts that constitute them, but they can also find applications in assembling other components connected to one or other of these parts, for example in automobile construction.
To enable them to be assembled by pressing, a hole is formed through the tubular part, perpendicular to its lengthwise direction and adapted to envelope the overall contour of the cylindrical part, and the cylindrical part and the tubular part are conjointly subjected, for example in a press, to a relative movement such that the cylindrical part is forcibly inserted into the hole in the tubular part from one side of the latter with the tubular part braced externally on the opposite side.
Various problems have to be overcome in carrying out pressing operations of this kind.
Firstly, to avoid deformation of the tubular part when the hole is formed in it, a machining process is normally required, with the cost penalty of using relatively complex and costly tooling.
Then, the tubular part forming two walls around its hole, by virtue of its tubular structure, the wall which is on the side from which the cylindrical part is inserted is the first to be subjected to the pressing force and therefore can itself be subject to some deformation.
If this occurs, the cross-section of the tubular part is modified around its hole and this can compromise the quality of the mechanical joint between it and the cylindrical part and therefore the durability of the assembly.
In any event, the resulting visible deformation of the tubular part is bound to cast some doubt on this durability and the assembly must therefore normally be discarded.
Furthermore, even in the absence of any deformation of either wall of the tubular part, the surface area of contact between the tubular part and the cylindrical part is reduced to that of the edge of the walls of the tubular part around its hole.
The quality of the mechanical joint is dependent on this contact surface area.
In practice, in some applications at least, in which the parts concerned are subject to a tear-out force and/or to vibrations, the contact surface area may be insufficient to assure a durable assembly.
To overcome this latter problem at least in part, Swiss patent No. 383 303 proposes the formation of an upstanding rim around the hole in at least one of the walls of the tubular part, in practice in both of them.
According to the above Swiss patent the tooling used for this purpose is a punch with a pointed end in the form of a blade so that, to form the upstanding rim, the wall concerned is simply pushed back laterally on either side of this blade.
As a result the upstanding rim obtained does not extend around all of the perimeter of the hole that it borders and its height varies between the two ends of the diameter of the hole, from a zero height at these two ends to the detriment of the reinforcement.
Moreover, and most importantly, the risk of deformation of one or other of the walls of the tubular part during pressing of the cylindrical part into the hole in the latter is virtually unchanged.